At present, in-cell touch screen has been widely used due to the advantages of realizing higher integration level of the whole panel, lightening and thinning the panel and the like as a result of integration in a sensing panel. The in-cell touch screen may be integrated with touch and sensing functions. FIG. 1 is a structural schematic diagram of a touch sensing circuit in the prior art. As shown in FIG. 1, the touch sensing circuit includes data lines, a first gate line, a second gate line, a signal transmission line, a liquid crystal capacitor Clc, a storage capacitor Cst, a common electrode, a signal processor, a thin film transistor T1 and a thin film transistor T2, wherein the source of the thin film transistor T1 is connected to the data lines, the gate of the thin film transistor T1 is connected to the second gate line, the drain of the thin film transistor T1 is connected to the source of the thin film transistor T2, the drain of the thin film transistor T2 is connected to the signal transmission line, and the gate of the thin film transistor T2 is connected to the first gate line. A second node P is formed at a junction of the thin film transistor T1 and the thin film transistor T2. The second node P is connected to one end of the liquid crystal capacitor Clc and one end of the storage capacitor Cst, while the common electrode is connected to the other end of the liquid crystal capacitor Clc and the other end of the storage capacitor Cst. The voltage provided by the common electrode is Vcom. FIG. 2 is a schematic diagram of an arrangement of liquid crystal of a liquid crystal panel when no touch is performed, and FIG. 3 is a schematic diagram of an arrangement of the liquid crystal of the liquid crystal panel when a touch is performed. It can be seen from FIG. 2 and FIG. 3 that, as the liquid crystal is an anisotropic medium, the liquid crystal capacitor Clc is related to the orientation and spacing of liquid crystal molecules. When a liquid crystal panel is touched, the capacitance of the liquid crystal capacitor Clc will be changed while the capacitance of the storage capacitor Cst will not be changed.
As shown in FIG. 1, the working principle of the touch sensing circuit is as follows: assuming that a voltage written into a pixel unit in a previous frame is Vp, the charge stored in the liquid crystal capacitor Clc and the storage capacitor Cst is:Qp=Vp*(Cst+Clc).When a high level is applied to the first gate line, the thin film transistor T2 is turned on, the voltage Vp at the second node is transmitted to the signal processor 101 via the signal transmission line, and then the signal processor compares the voltage Vp at the second node P with a reference voltage Vref so as to judge whether a touch is performed. Specifically, when no touch is performed, the voltage at the second node P is Vp; and when a touch is performed, the change in capacitance of the liquid crystal capacitor Clc is ΔClc, and the voltage at the point P is changed to Vp1′F=Vp*Clc/(Clc+ΔClc) according to the principle of charge conservation, so that the change in voltage at the point P when a touch is performed and when no touch is performed is:ΔVp=Vp1′−Vp≈Vp*ΔClc/(Cst+Clc)/(Cst+Clc).
It can be seen from the above equation that the value of ΔVp1 directly determines the sensitivity of touch detection.
The prior art has the following problem: the change ΔVp1 in voltage at the point P when a touch is performed and when no touch is performed is too small, thereby the sensitivity of touch sensing is reduced.